The separation of various substances through selective absorption using a simulated moving bed of adsorbent is an example of a process in which an axial multiport rotary valve is useful. Simulation of a moving adsorbent bed is described in U.S. Pat. No. 2,985,589 (Broughton et al.), which is mentioned above. FIG. 1 depicts process and apparatus of this patent. In accomplishing this simulation, it is necessary to connect a feed stream to a series of beds in sequence, first to bed no. 1, then to bed no. 2, and so forth for numerous beds, the number of beds often being between 12 and 24. These beds may be considered to be portions of a single large bed whose movement is simulated. Each time the feed stream destination is changed, it is also necessary to change the destinations or origins of at least three other streams, which may be streams entering the beds, such as the feed stream, or streams leaving the beds. The moving bed simulation may be simply described as dividing the bed into a series of fixed beds and moving the points of introducing and withdrawing liquid streams past the series of fixed beds instead of moving the beds past the introduction and withdrawal points.
The multiport rotary disc valve of Carson No. (3,040,777) provided a satisfactory valve design for the simultaneous interconnection of two independent groups of conduits such that each conduit of the first group could be brought into individual communication with every conduit of the second group. Upon reference to FIG. 1 and Broughton No. (2,985,589), it can be seen that there are two groups of conduits which need to be interconnected. One group consists of the conduits which provide the flows entering and leaving the simulated moving bed adsorbent system, that is, the flows which are switched among the beds, such as the feed stream. A second group consists of the conduits associated with the individual beds, that is, which supply and remove fluid from the beds, one conduit being connected between each two beds. It is to be noted that each conduit of the second group serves that dual function of supply and removal, so that it is unnecessary to provide conduits for supplying fluid separate from those for removing fluid.
There are many different process requirements in moving bed simulation processes, resulting in different flow schemes and thus variations in rotary valve arrangement. For example, in addition to the four basic streams described in Broughton No. (2,985,589), it may be desirable to utilize one or more streams to purge, or flush, a pipeline or pipelines. A flush stream is used to prevent undesirable mixing of components. The flush substance is chosen to be one which is not undesirable for mixing with either main stream, that being purged or that which enters the pipeline after flushing is completed. U.S. Pat. No. 3,201,491 (Stine et al.) may be consulted for information on flushing lines as applied to the process of Broughton No. (2,985,589). It may be desirable to pass fluid through a bed or beds in the reverse direction from normal flow. This is commonly known as backflushing, a subject treated in U.S. Pat. No. 4,319,929 (Fickel).
Multiport rotary disc valves of the general arrangement shown in the above-mentioned U.S. Pat. Nos. (3,040,777 and 3,422,848) have been fabricated in various sizes up to valves utilizing 41/2 foot diameter rotors. These valves have seven concentric circumferential grooves, or tracks, and 24 ports spaced around the periphery of the stator. A single valve of this size weighs approximately 26,000 pounds, has an overall height of about 15 feet, and occupies a plan area of approximately 81/2 by 81/2 feet. These figures do not include a separate hydraulic power unit used with the hydraulically driven actuator mounted on the valve proper. It can be appreciated that it is desirable to use apparatus of less bulk and weight to accomplish the same functions; the present invention provides such a smaller rotary valve.
It is highly desirable to use a single device to simultaneously transfer all of the fluid streams, thereby avoiding the obvious problems associated with numerous separate valves which must be simultaneously actuated.